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安大略省马拉松附近的赫姆洛金矿床是现今北美最大的金矿之一。矿床呈层状产于太古代变质火山沉积岩中,主矿带由黄铁绢云片岩和块状重晶石组成。赫姆洛西部其它重晶石产地虽有发现,但北美太古界产出层状重晶石还是首次报道。矿床大量富集Au、Mo、Sb、Hg、Tl和V,碳酸盐缺乏。因变形、变质作用的影响,至今未能确定矿床成因。矿床钻孔剖面中Au品位与黄铁矿的硫同位素组成相关。这一事实以及具同位素分馏的硫化物与硫酸盐共生,表明金与黄铁矿、重晶石是同时沉淀的。剖面间硫同位素和硫矿物的不对称分布连续,以及赫姆洛矿区与其西部地区重晶石中同位素组成的相似性都与同生沉积矿床的模式相吻合。硫矿物的形成有两种可能,一是来自有限盆地的外生硫酸盐在某个地热系统中部分还原形成贫~34S的硫化物;其二,硫酸盐和硫化物都是岩浆热液成因的。硫酸盐和具同位素分馏的硫化物在太古代岩石中均属罕见,但在太古代大型金矿床中却异乎寻常地或一或同时出现。因此,含有硫酸盐,并在氧化态、还原态硫之间能发生同位素分馏的这样一种适当的高fo_2值的热液可能利于金的溶解、迁移、沉淀。
The Hermosa gold deposit near the Ontario Marathon is one of the largest gold mines in North America today. Deposits are stratified in the Archean metamorphic volcanic sedimentary rocks, the main belt by the yellow sericite schist and massive barite composition. Although other barite areas in the western region of Helmrode have been discovered, layered barite from North Pacific Archean is still the first to be reported. The deposit is rich in Au, Mo, Sb, Hg, Tl and V, carbonate deficiency. Due to deformation and metamorphism, so far the cause of the deposit has not been confirmed. The Au grade in the borehole profile correlates with the sulfur isotopic composition of pyrite. This fact, as well as isotopic fractionation of sulfides with sulfates, suggests that gold and pyrite and barite precipitate simultaneously. The continuous asymmetric distribution of sulfur isotopes and sulfur minerals in the section and the similarities of the isotopic composition of barite in the Hemilo mining area and its western area are consistent with the patterns of sedimentary deposits in the same area. There are two possibilities for the formation of sulfur minerals. One is that exogenous sulfates from limited basins are partially reduced to form ~ 34S-depleted sulfides in a geothermal system. Second, sulfates and sulfides are all causative of magmatic hydrothermal fluids . Sulfates and isotopic fractionated sulfides are rare in the Archean rocks, but unusually or simultaneously or simultaneously in large Archean gold deposits. Therefore, such a suitable high fo_2 value hydrothermal fluid containing sulfate and capable of isotopic fractionation between the oxidized and reduced sulfur may be beneficial to the dissolution, migration and precipitation of gold.